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Subconscious Signals Can Trigger Brain's Drug-Craving Centers

Quick flashes of cocaine-related photos—so brief viewers don’t even realize what they’re seeing—can instantly trigger “reward circuitry” in the brains of drug-addicted patients, activating the same brain regions that respond to sexual images. Researchers say their findings may provide new clues for treating addictions and possibly other conditions, like eating disorders, that are marked by uncontrolled desires and behaviors.

The idea that we’re often motivated by unconscious fears
and desires has been around for more than a century, but it’s
been difficult for scientists to determine how such unconscious
factors affect the brain. In a new study, a research team led
by Drs. Anna Rose Childress and Charles O’Brien at the
University of Pennsylvania School of Medicine used neuroimaging
to look at how specific brain regions respond to different types
of unconscious cues. Their research, funded by NIH’s National
Institute on Drug Abuse (NIDA), was published in the June 30,
2008, issue of the journal PLoS One.

The scientists used functional MRI to scan the brains of 22
men—all under treatment for cocaine addiction—while
they viewed a series of images. Test images flashed by in just
33 milliseconds—so quickly that the patients were not consciously
aware of them. The images included drug-related visuals—like
crack pipes or chunks of cocaine—as well as sexual, disturbing
and neutral images. Each test image was immediately followed
by a longer view—lasting nearly a half-second—of
a neutral image, such as household objects or outdoor scenes.
Although patients could consciously recall only the longer-lasting
images, their brain scans revealed responses to the “unseen” test
images.

The unseen drug photos stimulated reward circuits within the
brain’s limbic system, a primitive network involved in
emotion and reward and also implicated in drug-seeking and craving.
These activated brain regions overlapped substantially with those
activated by sexual images. This finding supports the idea that
addictive drugs take over the brain’s reward circuits that
normally respond to cues for natural rewards needed for survival,
like food and sex.

To verify that the brain’s responses to unseen drug cues
reflected the patients’ conscious feelings about drugs,
some of the volunteers were given a different test 2 days later.
They were asked to take a longer look at some of the test images,
and their emotional responses were assessed. Those with the strongest
brain responses to unseen drug cues in the earlier test also
had the strongest positive associations to these visible drug
cues.

“This is the first evidence that cues outside one’s
awareness can trigger rapid activation of the circuits driving
drug-seeking behavior,” said NIDA Director Dr. Nora Volkow. “Patients
often can’t pinpoint when or why they start craving drugs.
Understanding how the brain initiates that overwhelming desire
for drugs is essential to treating addiction.”